A semiconductor device and a flat panel display device are formed through deposition and etching of a plurality of thin films on a substrate. That is, a thin film is deposited in a predetermined region, generally in the central region, on a substrate, and a portion of the thin film in the central region of the substrate is removed by an etching process using an etching mask, whereby a device having a predetermined thin film pattern is manufactured.
However, during deposition of a thin film, because the thin film is formed on the entire surface of the substrate, and the thin film in only the central region of the substrate is targeted for etching, the thin film on the edges of the substrate is not removed and is left remaining, and particles accumulate on the edges of the substrate during etching. Moreover, because substrate supporters that support substrates typically employ electrostatic power or negative pressure to mount a substrate, the interface between the substrate and the substrate supporter is separated and develops gaps that cause particles and thin film to accumulate on the entire undersurface of the substrate.
Thus, when further processes are performed without removing the particles remaining on the substrate and the accumulated thin film, various unfavorable conditions may arise, such as warping of the substrate and the substrate becoming difficult to align.
Typically, methods for removing the above particles and accumulated thin film include wet etching that removes particles from a surface by immersing the latter in a solvent or rinse, and dry etching that removes depositions by etching a surface with plasma.
While wet etching is used to effectively remove particles deposited on a substrate surface, difficulties in process control substantially restrict localized removal from the undersurface of the substrate, and extensive use of processing chemicals increases fabrication cost and exacerbates waste disposal and environmental issues. Further, larger-scale equipment must be used when extensive processing time is required. Conversely, when dry etching using plasma is employed to remove thin films or particles on and under a substrate, the above-described limitations of wet etching may be resolved.
Accordingly, development of dry etching apparatuses for etching substrate undersurfaces is being intensely pursued.
Specifically, a related art plasma etching apparatus employing plasma to etch substrate undersurfaces is disclosed in U.S. Pat. No. 5,213,650, which is hereby incorporated in its entirety by reference.
In the above U.S. Pat. No. 5,213,650, an apparatus with a vacuum chamber is provided. Here, a space is defined between a plate and the front surface of a wafer, and reactive gas is discharged into the space. Plasma is generated at the rear surface of the wafer to perform etching.
In the above configuration, in order to support a wafer, when a lift pin is employed to support a substrate, the lift pin is disposed in the processing region on the rear surface of the substrate to induce an arc discharge during processing, so that the processing is impeded or the substrate can be damaged.
Furthermore, when a plurality of lift pins is used to support a substrate as in the above, the supported portions of the substrate, that is, the rear surface of the substrate in contact with the lift pins, are not etched. When subsequent processes are performed without etching of these areas, this may cause defects in the final product, or a separate etching process is required for the areas that have not been etched.
In addition, when a wafer is supported by only a lower pin, it is difficult to ensure stable mounting of the wafer, so that the wafer may be separated from the pin when subjected to vibrations.
In the above configuration, however, reactive gas is discharged into a space defined between a wafer and a plate, and etching is performed with plasma formed at a rear surface of the wafer. At the same time, plasma formed at the rear surface of the wafer is admitted to a front surface of the wafer with a thin film pattern, etc. formed thereon, or plasma is formed through gas discharge within that space to perform etching.
Accordingly, due to the etching of the front surface of the wafer, yield of finished products decreases and the rate of defects increases, or a separate member for protecting the front surface of the wafer from being etched is required to obviate the above.